1. Field of the Invention
The present invention relates to a printed wiring board including an electrically-conductive power supply layer and an electrically-conductive ground layer.
2. Description of the Prior Art
A printed wiring board usually includes an electrically-conductive power supply layer and an electrically-conductive ground layer. A LSI (Large-Scale Integrated circuit) chip is mounted on the surface of the printed wiring board. The LSI chip is connected to the electrically-conductive power supply layer and the electrically-conductive ground layer. A chip capacitor, namely a bypass capacitor, is connected to the electrically-conductive power supply layer and the electrically-conductive ground layer. The bypass capacitor serves to reduce power supply noise.
Japanese Patent Application Publication Nos. 6-244562 and 11-233951 disclose an island of an electrically-conductive power supply layer and an island of an electrically-conductive ground layer, for example. The bypass capacitor is connected to the power supply and ground layers through vias. In this case, power supply noise is allowed to spread over the entire power supply and ground layers. Power supply noise cannot sufficiently be reduced. The power supply noise causes radiation of electromagnetic waves from the printed wiring board.